Design Patterns Simplified - Part 6 (Prototype)

Prakash Tripathi

Design PatternPrototype PatternDeep CopyICloneableShallow Copy

22 Comments

Join the conversation! Your thoughts help the community grow.

Prakash Tripathi10y ago
Thnx Cao.
Cao Fangsheng10y ago
Good article.
Prakash Tripathi10y ago
Thnx Nagaraj.
Kuppurasu Nagaraj10y ago
Nice article..
Prakash Tripathi10y ago
Thnx Sibeesh.
Sibeesh Venu10y ago
Nice Share
Prakash Tripathi10y ago
Thnx Raja
Prakash Tripathi10y ago
Thnx Sreenivasa
Prakash Tripathi10y ago
Thnx Santhakumar
Raja T10y ago
Nice, thanks for sharing
sreenivasa k10y ago
very nice
Santhakumar Munuswamy10y ago
Thanks for nice share
Prakash Tripathi10y ago
Thnx Rupesh.
Rupesh Kahane10y ago
nice share..
Prakash Tripathi10y ago
Thnx Maruthi for bringing different point of view. Basically = operator doesn't work either with Shallow or Deep copied object as the object state is no longer the same. However it may work if you create copy like FourWheelar truckNew = car; but in this case any change made in the target object will also reflect in the source object including the Type, Brand and Model. You may test and let me know if you have different findings.
Prakash Tripathi10y ago
Thnx Ankur
Prakash Tripathi10y ago
Thnx Kiranteja
Prakash Tripathi10y ago
Thnx Humayun.
Maruthi Palllamalli10y ago
Condition missing your logic ... Please check this ---- FourWheelar car = new FourWheelar(); and FourWheelar truckNew = car.Clone() as FourWheelar; ---------------------- if(car==trucknew) { // same refrence found } else { // Refrence mismatched }............... if copied object having same refrence means , Why should i use another refrence variable to display truck details ? Why can't show car details with trucknew refrence varaible.
Ankur Mistry10y ago
Helpful stuff.
Kiranteja Jallepalli10y ago
great work prakash
Humayun Kabir Mamun10y ago
Nice...

I am here to continue the discussion around Design Patterns. Today we will discuss another creational design pattern called Prototype.

In case, you have not had a look at our previous articles, go through the following link:

Before talking about its implementation let’s begin with defining it.

Prototype is a design pattern which believes and enforces object cloning or copying over new object creation.

But object copy is that important

Answer is simple, copying objects improves performance in a situation when one needs lot of objects and creating them turns out to be a costly affair.

Since we are talking about copy let’s discuss shallow and deep copy as well.

Shallow Copy

As the name suggest, it’s a partial or incomplete copy and any reference types of the source object will not be copied and will keep on referring to the same memory location.

In .NET it is achieved by MemberwiseClone method.

Deep Copy

Similar to the name, it’s a real copy of all the members in the source object including reference types. For reference types, it creates a new memory location in heap to provide true copy experience.

We need to write custom code to achieve deep copy.

Now let’s talk about implementation of the pattern.

Assume we have an abstract class Vehicle that has the following structure,

internal abstract class Vehicle
{
internal string VehicleType
{
get;
set;
}
internal string Brand
{
get;
set;
}
internal string Model
{
get;
set;
}
internal abstract void ShowDetails();
internal abstract Vehicle ShallowCopy();
internal abstract Vehicle DeepCopy();
internal ExtraInformation MoreInfo = new ExtraInformation();
}

We can take interface as well but in that we need to override all the properties again which looks duplicate in this case.

Here class Vehicle works like prototype. We have added class ExtraInformation to depict deep copy and shallow copy concepts.

class ExtraInformation
{
internal string Cost { get; set; }
internal int Ratings { get; set; }
}

Now let’s have concrete prototype FourWheelar as in the following,

internal class FourWheelar: Vehicle, ICloneable
{
internal override Vehicle ShallowCopy()
{
return this.MemberwiseClone() as Vehicle;
}
internal override Vehicle DeepCopy()
{
Vehicle vehicle = this.MemberwiseClone() as Vehicle;
vehicle.MoreInfo = new ExtraInformation();
vehicle.MoreInfo.Cost = this.MoreInfo.Cost;
vehicle.MoreInfo.Ratings = this.MoreInfo.Ratings;
return vehicle;
}
internal override void ShowDetails()
{
Console.WriteLine(string.Format("Vehicle Type: {0} \tBrand: {1} \tModel: {2} \tCost: {3} \tRatings: {4}", this.VehicleType, this.Brand, this.Model, this.MoreInfo.Cost, this.MoreInfo.Ratings));
}
public object Clone()
{
return DeepCopy();
}
}

You can see here that we have also implemented ICloneable interface. To be frank, it’s not required here but I have added it to present its existence. It just have Clone method and when called, we are returning custom DeepCopy method.

So setup is done now, let’s use this in client.

static void Main()
{
Console.Title = "Prototype pattern demo";
FourWheelar car = new FourWheelar();
car.VehicleType = "Car";
car.Brand = "Maruti";
car.Model = "Swift";
car.MoreInfo.Cost = "6.5 Lakhs INR";
car.MoreInfo.Ratings = 2;
FourWheelar truck = car.ShallowCopy() as FourWheelar;
truck.VehicleType = "Truck";
truck.Brand = "Tata";
truck.Model = "ACE";
truck.MoreInfo.Cost = "4.5 Lakhs INR";
truck.MoreInfo.Ratings = 3;
Console.WriteLine("******************************Shallow Copy******************************");
Console.WriteLine("Origional Object:");
car.ShowDetails();
Console.WriteLine();
Console.WriteLine("Shallow Cloned Object:");
truck.ShowDetails();
}

Output

run

You can see here that when we change the cost and ratings in the target object, original object is also getting changed. This is happening because the copied object is still holding the same reference as source.

Now let’s test deep copy,

static void Main()
{
Console.Title = "Prototype pattern demo";
FourWheelar car = new FourWheelar();
car.VehicleType = "Car";
car.Brand = "Maruti";
car.Model = "Swift";
car.MoreInfo.Cost = "6.5 Lakhs INR";
car.MoreInfo.Ratings = 2;
FourWheelar truckNew = car.Clone() as FourWheelar;
truckNew.VehicleType = "Truck";
truckNew.Brand = "Tata";
truckNew.Model = "ACE";
truckNew.MoreInfo.Cost = "4.5 Lakhs INR";
truckNew.MoreInfo.Ratings = 3;
Console.WriteLine("******************************Deep Copy******************************");
Console.WriteLine("Origional Object:");
car.ShowDetails();
Console.WriteLine();
Console.WriteLine("Deep Cloned Object:");
truckNew.ShowDetails();
}

Output

Output

As you can see here that when we change the cost and ratings in the target object, original object is not getting changed. This is happening because the copied object is having new reference.

Hope you have liked the article. Looking forward for your comments/suggestions.